Looks easy, hurts really bad. Use this one as a warm-up or finisher. Check it out.

Though typically performed with just bodyweight, don't underestimate this exercise, especially as a primer for other quad exercises. It can also be used as a higher-rep finisher on leg day. The "burn" is intense.

The Peterson step-up encourages forward tracking of the knee over the toe, along with a ball-of-the-foot contact point of the working leg, both of which encourage quad activation with emphasis closer to the distal or knee end of the thigh.

Peterson Step-Up

Avoid pushing off the ground with the non-working leg. Let the working leg carry the entire load.

Stand up tall at the finish position.

Remember, the quads are knee extensors. To get the VMO to do the most work, squeeze the knee tight at the top. (Note: VMO is short for vastus medialis obliquus. This is the "teardrop" muscle located on the inside of the knee.)

Once the reps become easy, increase the range of motion with a higher step rather than add weight.

Be vigilant about your knee tracking. A good rep should show no compensatory action, like the knee falling inwards towards the midline of the body. The knee should point where the toe points at all times.